The invention relates to a liquid filter, particularly an oil filter for an internal combustion engine, comprising a housing with a concentrically disposed outlet opening for filtered liquid and at least one inlet opening for the liquid to be filtered, and a filter element sealingly disposed between the inlet opening and the outlet opening.
In the prior art, oil cartridge filters, also referred to as spin-on filters, are frequently used. These replaceable oil filters are preferably screwed directly onto the cylinder head of an internal combustion engine and are thus integrated into the oil circuit of the engine. To this end, an internal thread is provided in the cylinder head of the internal combustion engine into which a threaded nipple is firmly screwed having an external thread extending axially away from the cylinder head. The oil cartridge filter, comprising a cup-shaped housing and an end plate with a thread disposed concentrically therein, is in turn screwed onto this threaded nipple which is screwed into the cylinder head. It is necessary to use a threaded nipple because of production and material related difficulties that make it impractical to form an external thread directly on the cylinder head.
A drawback of this arrangement is that two pairs of threads must be used, namely, the cylinder head/threaded nipple thread pair on the one hand and the threaded nipple/oil cartridge filter thread pair on the other. This increases the possibility of leakage problems and also has drawbacks with regard to the diameter available for the outlet in the threaded interior. Another drawback is the relatively high cost of the threaded nipple.